Now is the time of summer festivals. Streets and parks throb with performers, singers, dancers, mimes or quickstretch charcoal artists. Tyros get their chances, veterans experiment, causes explode.

The afternoon Baltimore begins its third, most ambitious TNT - The New theater Festival - with a parade to be reviewed by the city's art-encouraging mayor, William D. Schaefer. Producer Al Kraizer calls TNT "America's only international theater festival of new performance arts."

Though next Sunday there will be street performance and workshops all around the Mount Vernon Place area. In various auditoriums, 20 visiting theater groups will present 150 formal performances. The visitors include Yoshi of Tokyo, the Netherlands' Gerardjan Rynder Workshop, the Actors Lab of Ontario, Atelier Theater et Musique of Paris, Le Plan K of Brussels, Warsaw Mime Theater, Harlem's National Black Theater, the Mabou Mines of New York, Knoxville's Playground B. Boston's Reality, Buffalo's American Contemporary theater, which fuses elements into what it designates as "holistic theater."

Baltimore's explosion can be traced back to a lake in New York, where Chautauqua was founded in 1874.

Long before the auto, movies and TV, the New York summer colony became the crown of a circuit that entertained, or, as the preferred word was, "instructed," 19th-century vacationers. The remarkable thing about Chautauqua is that it's still operating, presenting symphony, opera and drama for a season that starts June 27 to run through Aug. 18. Chautauqua is summer home to the Cleveland Play House.

When it comes to festivals, the creamiest, most gitteringly professional on this continent is the Stratford Festival of Ontario. Mind your fishing manners, but take note of how a newspaperman's dream evolved 26 years ago and spread through arts-conscious Canada.

His name is Tom Patterson, and because he lived and worked in a stolid, fading railway center called Stratford - which inevitably labelled its little river the Avon - Patterson conceived the idea of a canvas theater for the plays of Shakespeare. Starting at the top, Patterson approached England's noted director, Tyrone Guthrie, who caught Patterson's enthusiasm. So did two major stars, Alse Guinness and Irene Worth. Their initial six-week season in a tent has balloomed into a fabulous three-theater, 23-week season.

Last week Stratford kicked off a fantastic parade: The Merry Wives of Windsor," "Macbeth" "The Winter's Tale," "As You Like It," "The Devils," "Uncle Vanya," "Judgement" and "Candide," - nine productions opening within five days. Later will be added "Julius casear," "Titus Andronicus," "Heloise and Abelard," "Private Lives," "Devotion," "Haworth - A Portrait of the Brontes," Ned and Jack," "Medea," a bill of four Beckett plays and Tom Cone's new "Stargazing."

Stratford's strength is quality in all areas, from lighting and costumes to acting and concepts, and its casts headed by Maggie Smith, Brian Bedford, Douglas Rain, Martha Henry and William Hutt. The first year's 42 performances grossed $206,000 last summer brought 300 additional perfomances and over $4 million more. Nation, province, township and scores of foundations contribute millions. Because people find Stratford, 65 miles from Toronto, a lively place to live now, over 33 firms have relocated industries there.

Stratford's influences permeates Canada. Into its 17th year Niagara-on-the-Lake's Shaw Festival. It's a small town of placid charm and the festival that began in its old courthouse now has its own theater and subsidiary events. "Major Barbara," "Heartbreak House," Ibsen's "John Gabriel Borkman" and Mary Elizabeth Braddon's old melodrama, "Lady Audley's Secret," from this summer's bill with Kate Reid, Douglas Campbell, Frances Hyland, Amelia Hall and Tom Kneebone in the casts.

In Stratford, Conn, the American Shakespeare Theater will resume next month after a blank 1977 summer. Gerald Freedman is its new artistic director, presenting Lynn Redgrave in "Twelfth Night" to run by July 5-Aug. 6, with "Coriolanus" or "Much Ado About Nothing" to follow. Freedman has a tough challenge to revive Lawrence Langner's playhouse on the Housatonic.

In New York's Central Park, "All's Well That Ends Well," with Elizabeth Wilson and Remak Ramsey, plays June 29-July 30 and "The Taming of the Shrew," releasing Raul Julia briefly from "Dracula" with Meryl Streep as his Kate, will run Aug. 3 through Sept. 3.

Head south.

South is the territory of the outdoor dramas - musical plays about history indigenouse to their [WORD ILLEGIBLE] . They began with Paul Green's "The Lost Colony," into its 38th summer the end of this month at Roanoke Island, N.C. There are scores of them on local themes stretching through the Smokies to Texas and Florida.

While in Florida, visit in 18th-century Italian theater. This gem of intimacy was brought, piece by piece, to Sarasota through circus man John Ringling's [WORD ILLEGIBLE] for picking up whatever caught his fancy. It was built in Asolo, 20 miles from Venice, in 1863, and Eleanora Duse would call it her "home stage."

Now, sealed into the air-conditioned Ringling Museum, Asolo is the home stage of the State Theater of Florida. Presently in repertory through Sept. 2 are "The School for Wives," "She Stoops to Conquer," "Travesties," "Richard III" and "The Man Who Came to Dinner."

When it seems that a new festival has just been born, you may find it's been there for years.

If you think of Shakespeare in Alabama as a novelty, think again. The Alabama Shakespeare Festival at Anniston is starting its seventh summer on July 14 with "Othello," a season that will run through Aug. 19 to include "The Merchant of Venice," "Measure for Measure," "Private Lives," "Clarence Darrow" and "A Lover's Complaint." Producer Martin Platt's company includes Philip Pleasants, Sidney Lloyd Hibbert and Gerald Holmes, the onetime Wolf Trap director.

At University Park, Pennsyivania State University is into its 21st summer for what is now is called the Nittany Mountain Summer Festival. There are two stages, alternating "The Sunshine Boys," "candide," "Lu Ann Hampton Laverty Oberlander" and a new play by Samuel Gallu, "An Offer You Can't Refuse." The autor of "Give'em Hell, Harry," which Kevin McCarthy has been playing in Boston, has written another one-character work in which Edward Binns plays a Mafloso figure. The Nittany Festival beigns June 22.

Increasingly alert to the performing arts, Duke University begins an American Dance Festival in Durham, N.C., June 18 with such noted companies as Eliot Feld's, Twyia Tharp's, Paul Taylor's and Pilobolus.

At Yorktwon, Va., in its historic Nelson House, there will be two alternating casts from Virginia Commonwealth University in "Where Two Chimneys Rise" under auspices of the National Park Services.

In Abingdon, Va, the Highland Festival is one production of the Barter Theater - Virginia's State Theater - which new operates in two playhouses furnished with seats and decor from New York's vanished historic Empire Theater and the boast is "four plays in three days."

These are only East Coast jottings. Head west and you'll note that Ann Arbor is into its 50th summer festival with four plays in repertory.

Illinois is starting a new festival in the hometown of Frank Lloyd Wright, Ernest Hemingway and Edgar Rice Burroughs, strange bedfellows but enough to inspire the Oak Park Festival for house tours and a production of "Othello" July 11 through 30, though no one claims that he lived in Oak Park.

The Minneapolis Tyrone Guthrie opened its summer with an American premiere for Henrik Ibsen. That may be a century late for "The Pretenders" but its solid Scandinavian territory. In its cast will be Randall Duk Kim, who also will be acting Hamlet, in the Guthrie's eigth-play line-up.

San Diego's Old Globe Theater was destroyed by fire in March but by that night the company had a temporary new home. The planned season will go on and eventually, its directors vow, the Old Globe will be housed "In far fairer manner." Playing this summer are "Henry V," "A Midsummer Night's Dream" and "The Winter's Tale."

Head up to Oregon for this country's strongest, most reliable, non-tinkered-with Shakespeare, Ashland's Oregon Festival. It now has three stages. Running through Sept. 24 will be "The Taming of the Shrew," "Tartuffe," "Mother Courage," "Timon of Athens," "Miss Julie," "Richard III," "The Tempest" and a new experimental play in the new playing space, the Black Swan.

The other direction, across the Atlantic?

Europe bristles with festivals, but did you know that in the Schloss-Spiele Heidelberg Castle Festival every Friday and Saturday night in August, the bill is Romberg's "The Student Prince"?